Hydrofoil-shaped stabilizing or attitude-affecting means for boats

ABSTRACT

A hydrofoil-shaped stabilizer or attitude-changing means for boats, having an elongated frame assembly adapted to be connected to a submerged portion of the hull of a boat with its longitudinal axis parallel to the fore-to-aft axis of the boat. A flexible curtain assembly extends about the frame assembly and is fixed thereto but free to move laterally and to a more limited extent longitudinally relative to the frame assembly. The interior of the curtain assembly communicates with the surrounding water and is deflected to one side or the other relative to the frame assembly by its displacement relative to the water caused by a change in the attitude of the boat so as to form a hydrofoil having a camber for generating forces to oppose the change in attitude to one side or the other when the boat is underway.

United States Patent [191 Burtis HYDROFOlL-SHAPED STABILIZING ORATTITUDE-AFFECTING MEANS FOR BOATS [76] Inventor: Samuel G. Burtis,Sherman Point Rd., P.O. Box 367, Camden, Maine 04843 [22] Filed: Nov.30, 1971 21 Appl. No.: 203,341

[56] References Cited UNlTED STATES PATENTS 3,118,639 Kiceniuk 115/28 A11] 3,753,415 1 Aug. 21, 1973 Primary Examiner-Milton Buchler AssistantExaminer-E. R. Kazenske Attorney-Edgar N. Jay

[5 7] ABSTRACT A hydrofoil-shaped stabilizer or attitude-changing meansfor boats, having an elongated frame assembly adapted to be connected toa submerged portion of the hull of a boat with its longitudinal axisparallel to the fore-to-aft axis of the boat. A flexible curtainassembly extends about the frame assembly and is fixed thereto but freeto move laterally and to a more limited extent longitudinally relativeto the frame assembly. The interior of the curtain assembly communicateswith the surrounding water and is deflected to one side or the otherrelative to the frame assembly by its displacement relative to the watercaused by a change in the attitude of the boat so as to form a hydrofoilhaving a camber for generating forces to oppose the change in attitudeto one side or the other when the boat is underway.

8 Claims, 7 Drawing Figures Patented Aug. 21, 1973 3,753,415

o 0 [IA 1- o 20 I6 I9 36 I7 35 3/ FIG6 35 FIG? HYDROFOIL-SHAPEDSTABILIZING R ATTITUDE-AFFECTING MEANS FOR BOATS This invention relatesto a water-borne vessel stabilizer or attitude-affecting means and, moreparticularly, to such a device which in response to forces generated bywater flowing thereover as when the boat rolls to one side or the other,varies its camber so that with the boat underway a force is generatedacting in the direction to oppose and retard the boats change inattitude whereby the motion of the boat is stabilized.

Widely different types of boat stabilizing systems utilizing fins orhydrofoils have hitherto been provided varying from relatively simplearrangements such as the modified centerboard of U.S. Pat. No.3,538,879, suited only for relatively small sailing boats, in which thecenterboard is intended to function as a stabilizing hydrofoil with amanually movable tail flap, to highly complex and costly systems inwhich fins (with or without adjustable tail flaps) are automaticallycontrolled in response to a sensor which may include one or moreacceleration responsive devices. However, such arrangements are veryoften either inadequate except for relatively small sailboats or arecomplex and require large amounts of power.

It is therefore a principal object of this invention to provide animproved boat stabilizer of very simple construction which, in responseto the roll of the boat to either side, automatically adjusts its camberto provide a hydrofoil shape which, with the boat underway, generatesforces to oppose and diminish the roll.

A more specific object is to provide such a stabilizer which does notrequire any parts to extend or, to be sealed through the hull of theboat and which .can be used to stabilize a wide variety of types andsizes of vessels.

ln carrying out the present invention, one or more stabilizer assembliesare mounted to extend longitudinally from fore to aft along the centerline of the vessel. Instead or in addition, such stabilizers can bemounted on the bilges symetrically spaced from the center line. Eachstabilizer has a central or inner frame structure fixed to the hull ofthe boat which supports a flexible wall or curtain assembly forming anenclosure therefor which is free to move laterally with respect theretoand, to a more limited extent, is free to move fore to aft relative toits inner supporting structure all in response to the transverse flow ofwater relative to the stabilizer assembly caused by rolling of thevessel. When the vessel is underway with little or no rolling, theflexible wall of the stabilizer assumes its neutral position withsubstantially equal camber on both sides of the stabilizer. As thevessel rolls to one side or the other assuming an initially vertica'attitude, transverse displacement of the flexible wall of eachstabilizer assembly alters the camber thereof so that the upwardlypresented surface of the wall forms a shorter fore-to-aft stream linethan the downwardly presented surface. Consequently with the vesselunderway, the forces generated act on the stabilizer in the direction tourge it downward and thus to oppose the roll of the vessel.

The foregoing as well as additional objects and advantages of thepresent invention will be apparent from the following description of apreferred embodiment and the accompanying drawing in which shapedstabilizer mounted on the keel thereof with its port side presented toview;

FIG. 2 is a front elevational view of the stabilizer shown in FIG. 1;

FIG. 3 is a side elevational view thereof with its starboard sidepresented to view;

FIGS. 4 and 5 are cross-sectional views taken respectively through thelines 4-4 and 5-5 of FIG. 3;

FIGS. 6 and 7 are views taken from above similar to FIG. 5 butdiagrammatic for convenience and showing the operation of the stabilizerjust after the start of a roll to the right (starboard) and a roll tothe left (port) respectively.

Referring now to the drawings, stabilizer assembly 10 is a preferredembodiment of my invention which I have found well suited for use on apower cruiser boat having a semi-displacement type hull with a softchine, an overall length of about 37 feet, a maximum beam of about 12feet 4 inches, a displacement of about 1 1 tons, and a cruising speed ofabout 10 to 11 knots. I have mounted and used successfully two suchstabilizer assemblies 10 in line along the keel 11 of the boat 12. Whilemy invention will now be described in detail in connection with suchstabilizer assemblies 10 (only one of which is shown in the drawing), itis to be understood that variations in the design shown can be made, andother materials than those designated can be used without departing frommy invention.

Stabilizer assembly 10 comprises a top plate 14 fixed to the bottom ofthe keel 1 1 by means of a pair of elongated clamps 15 preferably formedof suitably treated wood such as oak to which the top plate 14 is boltedand which are in turn bolted to opposite sides of keel 1 1. Fixed to thetop plate 14 are frame members 16, 17, 18, 19 and 20 which depend fromthe top plate 14 and are arranged in spaced relation from fore to aft inthe sequence stated. The bottom ends of the frame members 16-20 aresecured to a bottom plate 21. Preferably, for reasons to be pointed outhereinbelow, upper and lower auxiliary plates 22 and 23 are respectivelyinterposed between the upper and lower ends of the frame members and thetop and bottom plates 14 and 21.

The spacing between adjacent frame members 16-20 is not critical, butshould be enough to permit free lateral displacement of the water withinthe enclosure formed by the flexible curtain assembly 30 yet to bedescribed as well as to facilitate mounting and operation of theflexible curtain assembly 30.

The frame members 16-20 can be formed of any material suitable formarine use, but preferably are built up of marine plywood laminated witha suitable marine glue and are bored for the passage therethrough ofbronze carriage bolts by which they and the various plates are fastenedtogether. Other materials contemplated for use in making the framemembers 16-20 are bronze or suitably reinforced fiber glass constructedto readily break away in the event the stabilizer assembly shouldcollide with an obstruction in spite of its advantageously short span.Before the lower auxiliary plate 23 and the bottom plate 21 are fixed tothe lower ends of the frame members 16-20, the flexible curtainassembly, which will now be described in detail. is

FIG. 1 is a perspective view broken away for convenience of a preferredembodiment of the present invention showing the hull of a vessel with ahydrofoilmounted on the frame members.

The flexible curtain assembly 30 comprises a wall or curtain member 31formed of flexible material sufficiently strong to withstand thesubstantial forces generated in operation and capable of effectivelypreventing the passage of water through it after long periods ofimmersion. I have found a three-ply fiber glass curtain memberreinforced with an epoxy resin provided satisfactory results. As shown,the height or vertical span of the curtain 31 is close to but just lessthan the distance between the top and bottom plates 14 and 21 so thatthe curtain 31 can move freely between them. At the same time, the spanof the curtain 31 should be sufficiently larger than the distancebetween the auxiliary plates 22 and 23 so that in its lateral movementin one direction or the other, motion of the curtain 31 is limited byits engagement on one side or the other with the corresponding sides ofthe plates 22 and 23. Along its forwardly presented vertical centerline, curtain 31 is fixed to the center of frame member 15 by bronzescrews 32.

Adjacent to its trailing edges, curtain 31 is provided with a pluralityof horizontally elongated openings 33 by means of which both sides ofcurtain 31 are movably connected to the trailing end portion of framemember 20 by fasteners 34 fixed to the frame member 20 and provided withoversize heads for retaining the curtain member 31 while leaving both ofits sides free to move fore and aft a limited extent. A plurality ofcross members or plates 35 extend between and are fastened to theopposite sides of the curtain 31 by means of elongated hinges 36. Thecross-members 35 are made of three-ply reinforced fiber glass, as in thecase of curtain 31, and each is riveted or otherwise suitably fastenedto its hinges 36 which in turn are, similarly fastened to the curtain.One of the cross-members 35 extends in the space between the framemembers 19 and 20 while the remainder extend two by two in spacedrelation in the remaining three spaces between the frame members 16-17,17-18, and 18-19.

As is shown most clearly in FIG. 5, the lengths of the cross-members 35are varied from front to back so that the curtain 31 when at rest in itscentral neutral position provides a well streamlined shape in the wateras the boat 12 moves ahead. Assuming no substantial relative lateralmotion between the stabilizer 10 and the water passing under the boat asit moves ahead, the curtain 31 remains substantially centrally disposedabout the frame members because of the crossmembers 35 and its owninherent stiffness. Because the curtain 31 is fixed to the frameassembly 24 only along its forward vertical center line, it is free tomove to a limited extent to one side or the other, when the boat beginsto roll, under the influence of the water which then, in addition to itsfore-to-aft motion relative to the boat and the stabilizer, also has asubstantial transverse component whereby the curtain 31 is forced to theright relative to the frame assembly 24 at the start of a roll to theright and as observed from above. (It is to be noted that in the sake ofclarity all references to the right or left of or in relation to thestabilizer 10 throughout this application will correspond to thestarboard and port sides respectively of the boat, that is to say as thestabilizer is observed from above by an observer facing the bow of theboat.)

At the start of a roll to the right, the curtain 31 is shifted from itscentral neutral position shown in FIGS. 2 and to the position shown inFIG. 6 with substantially increased camber on the now downwardlypresented right side and with the upwardly presented left side ofcurtain 31 engaging the left side of the frame members 16-20. Thus,stabilizer 10 provides a hydrofoil of small aspect ratio. While thedimensions are not at all critical, it may be well to note that in thestabilizer assemblies tested, the span L (FIG. 3) equaled about 13inches and the length of the chord C" (FIG. 5 was about 37 inches sothat the aspect ratio (L/C) was therefore 13/37. The length of the chordof the stabilizer corresponds substantially to the length of either sideof the frame assembly 24. It may be also well to note that the width offrame members 16, 17 and 18 was about 3 inches, and the width of thewidest plates 35 was such that the outside width of the curtain 31 was4% inches.

Assuming the condition of the sea in which the boat is moving ahead wassuch as to induce a 15? roll to starboard, the configuration of thestabilizer, until the start of the return roll, in view of the increasedlength of the streamlines along the downwardly presented surface ofcurtain 31 and the minimized length of the stream lines along itsupwardly presented surface results in a net average downwardly force onthe stabilizer in a direction to oppose the roll of the boat to theright.

At the start of the return roll, the relative lateral motion between thewater and the stabilizer is reversed and while the boat is rolling backto its vertical position and on into its roll to the left, the camber ofthe stabilizer is reversed as shown in FIG. 7 so that the return rolland the roll to the left are' also opposed by the forces acting on thestabilizer.

The volume within the curtain 31 is filled with water during operation.With the pressure differential across the stabilizer generated inkeeping with Bernoullis theorem, the effect thereof would be diminishedto the extent that water from the high pressure side (the upwardlypresented surface as seen in FIG. 6 and the downwardly presented surfaceas seen in FIG. 7) could flow through the stabilizer to the low pressureside. However, the upper and lower auxiliary plates 22 and 23 functionto impede the transverse flow of water because of theengagementtherewith of the upper and lower peripheral portions of thecurtain 31 on the high pressure side of the assembly. It may also bewell to note here that on each side, the shape of the auxiliary platesconforms to the chord of the hydrofoil shape formed by the actuatedcurtain assembly 30 so that in forming a stop for the edges of thecurtain, the auxiliary plates 22 and 23 not only prevent transverse flowof water but also aid in ensuring the desired foil shape.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and de-scribed or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

I claim:

1. A hydrofoil-shaped attitude-affecting means for a boat, comprisingelongated mounting means, means for connecting said mounting means tothe hull of a boat with the longitudinal axis of said mounting meansextending substantially parallel to the fore-to-aft axis of said boat, alongitudinally extending frame assembly connected to and depending fromsaid mounting means so as to be normally submerged in use, flexiblecurtain means substantially enclosing both sides of said frame assembly,means supporting said flexible curtain means so that the later is freefor limited lateral displacement to either side relative to said frameassembly between two extreme positions in response to and depending uponthe direction of the displacement of said frame assembly and flexiblecurtain means relative to the water surrounding the same, the interiorof said flexible curtain means being free to communicate with the watersurrounding the same when the latter is submerged, said flexible curtainmeans in said one of its extreme positions has one side thereof engagingone side of said frame assembly and the other side thereof spaced fromthe other side of said frame assembly, said flexible curtain means insaid other of its extreme positions has its other side engaging theother side of said frame assembly and said one side of said flexiblecurtain means is spaced from said one side of said curtain assembly, andsaid flexible curtain means in cooperation with said frame assembly inone of its said extreme positions having a camber for generating forcesin one direction normal to the longitudinal axis thereof and in theother of its said extreme positions having a camber for generatingforces in the direction opposite to said one direction, whereby saidattitude-affecting means functions on a boat underway ahead to inhibitchanges in the attitude thereof.

2. A hydrofoil-shaped boat stabilizer, comprising elongated mountingmeans, means for connecting said mounting means to the normallysubmerged portion of the hull of a boat with the longitudinal axis ofsaid mounting means extending substantially parallel to the fore-to-aftaxis of said boat, a longitudinally extending frame assembly connectedto and depending from said mounting means, flexible curtain meanssubstantially enclosing both sides of said frame assembly, meanssupporting said flexible curtain means so that the later is free forlimited lateral displacement to either side relative to said frameassembly between two extreme positions in response to and depending uponthe direction of the displacement of (a) said frame assembly andflexible curtain means relative to (b) the water surrounding the same,the interior of said flexible curtain means being free to communicatewith the water surrounding the stabilizer when the latter is submerged,said flexible curtain means in said one of its extreme positions has oneside thereof engaging one side of said frame assembly and the other sidethereof spaced from the other side of said frame assembly, said flexiblecurtain means in said other of its extreme positions has its other sideengaging the other side of said frame assembly and said one side of saidflexible curtain means is spaced from said one side of said curtainassembly, and said flexible curtain means in cooperation with said frameassembly in one of its said extreme positions having a camber forgenerating forces in one direction normal to the longitudinal axisthereof and in the other of its said extreme positions having a camberfor generating forces in the direction opposite to said one direction,whereby said stabilizer functions on a boat underway ahead to inhibitrolling thereof and thereby stabilize the same.

3. A stabilizer as set forth in claim 2 wherein means are provided forinhibiting the movement of water from along one side of said curtainmeans into the interior thereof while said curtain means is in each ofits said two extreme positions.

4. A stabilizer as set forth in claim 3 wherein said means forinhibiting the movement of water comprises a pair of auxiliary platesfor engaging the upper and lower peripheral portions of said curtainmeans along one side of said curtain means depending upon which of saidextreme positions is occupied by said curtain means.

5. A stabilizer as set forth in claim 2 wherein said curtain meanscomprises two water-impervious courses one extending along each side ofsaid frame assembly, and a plurality of cross-members extending betweenand pivotally connected to said courses.

6. A stabilizer as set forth in claim 5 wherein said curtain means isfixed to said frame assembly substantially only along the forwardlypresented vertical center line thereof.

7. A stabilizer as set forth in claim 5 wherein said frame assemblycomprises a plurality of -spaced frame members depending from saidmounting means and aligned along said longitudinal axis, and saidcrossmembers extend between said frame members.

8. A stabilizer as set forth in claim 7 wherein said curtain means isfixed to the forward one of said frame members substantially along thevertical center line thereof, and the rearward end portion of saidcurtain means is movably connected to the rearmost one of said framemembers and is free for limited longitudinal movement with respectthereto.

1B l l

1. A hydrofoil-shaped attitude-affecting means for a boat, comprisingelongated mounting means, means for connecting said mounting means tothe hull of a boat with the longitudinal axis of said mounting meansextending substantially parallel to the fore-to-aft axis of said boat, alongitudinally extending frame assembly connected to and depending fromsaid mounting means so as to be normally submerged in use, flexiblecurtain means substantially enclosing both sides of said frame assembly,means supporting said flexible curtain means so that the later is freefor limited lateral displacement to either side relative to said frameassembly between two extreme positions in response to and depending uponthe direction of the displacement of said frame assembly and flexiblecurtain means relative to the water surrounding the same, the interiorof said flexible curtain means being free to communicate with the watersurrounding the same when the latter is submerged, said flexible curtainmeans in said one of its extreme positions has one side thereof engagingone side of said frame assembly and the other side thereof spaced fromthe other side of said frame assembly, said flexible curtain means insaid other of its extreme positions has its other side engaging theother side of said frame assemblY and said one side of said flexiblecurtain means is spaced from said one side of said curtain assembly, andsaid flexible curtain means in cooperation with said frame assembly inone of its said extreme positions having a camber for generating forcesin one direction normal to the longitudinal axis thereof and in theother of its said extreme positions having a camber for generatingforces in the direction opposite to said one direction, whereby saidattitude-affecting means functions on a boat underway ahead to inhibitchanges in the attitude thereof.
 2. A hydrofoil-shaped boat stabilizer,comprising elongated mounting means, means for connecting said mountingmeans to the normally submerged portion of the hull of a boat with thelongitudinal axis of said mounting means extending substantiallyparallel to the fore-to-aft axis of said boat, a longitudinallyextending frame assembly connected to and depending from said mountingmeans, flexible curtain means substantially enclosing both sides of saidframe assembly, means supporting said flexible curtain means so that thelater is free for limited lateral displacement to either side relativeto said frame assembly between two extreme positions in response to anddepending upon the direction of the displacement of (a) said frameassembly and flexible curtain means relative to (b) the watersurrounding the same, the interior of said flexible curtain means beingfree to communicate with the water surrounding the stabilizer when thelatter is submerged, said flexible curtain means in said one of itsextreme positions has one side thereof engaging one side of said frameassembly and the other side thereof spaced from the other side of saidframe assembly, said flexible curtain means in said other of its extremepositions has its other side engaging the other side of said frameassembly and said one side of said flexible curtain means is spaced fromsaid one side of said curtain assembly, and said flexible curtain meansin cooperation with said frame assembly in one of its said extremepositions having a camber for generating forces in one direction normalto the longitudinal axis thereof and in the other of its said extremepositions having a camber for generating forces in the directionopposite to said one direction, whereby said stabilizer functions on aboat underway ahead to inhibit rolling thereof and thereby stabilize thesame.
 3. A stabilizer as set forth in claim 2 wherein means are providedfor inhibiting the movement of water from along one side of said curtainmeans into the interior thereof while said curtain means is in each ofits said two extreme positions.
 4. A stabilizer as set forth in claim 3wherein said means for inhibiting the movement of water comprises a pairof auxiliary plates for engaging the upper and lower peripheral portionsof said curtain means along one side of said curtain means dependingupon which of said extreme positions is occupied by said curtain means.5. A stabilizer as set forth in claim 2 wherein said curtain meanscomprises two water-impervious courses one extending along each side ofsaid frame assembly, and a plurality of cross-members extending betweenand pivotally connected to said courses.
 6. A stabilizer as set forth inclaim 5 wherein said curtain means is fixed to said frame assemblysubstantially only along the forwardly presented vertical center linethereof.
 7. A stabilizer as set forth in claim 5 wherein said frameassembly comprises a plurality of spaced frame members depending fromsaid mounting means and aligned along said longitudinal axis, and saidcross-members extend between said frame members.
 8. A stabilizer as setforth in claim 7 wherein said curtain means is fixed to the forward oneof said frame members substantially along the vertical center linethereof, and the rearward end portion of said curtain means is movablyconnected to the rearmost one of said frame members and is free forlimited longitudinal movement with respect Thereto.